Spoiler alert! The following contains details about the ending of Avengers: Infinity War. Stop reading now if you don't want to know.

Ten years of Marvel movies have spawned a number of memorable superhero stories.

But all good things, even blockbuster sagas and rich character arcs, must come to some sort of an end. And Robert Downey Jr., Chris Hemsworth and Chris Evans, whose shoulders bore the foundation of the Marvel Cinematic Universe as Iron Man, Thor and Captain America respectively, all think Avengers: Infinity War and next year's fourth Avengers movie (May 3, 2019) mark the culmination of a long road.

While filming both projects back-to-back in Atlanta, Downey would host lunch gatherings with his co-stars. "I can’t count how many times when we looked at each other and went, ‘Man, can you believe this? This could be it,’ ” Hemsworth says.

Captain America (Chris Evans) has lost faith and trust in his superhero family as "Avengers: Infinity War" starts.(Photo: CHUCK ZLOTNICK)

In Infinity War, intergalactic bad guy Thanos (Josh Brolin) faces off with Marvel’s collected bunch of heroes, from the aforementioned elder statesmen to new blood like Spider-Man (Tom Holland) and Black Panther (Chadwick Boseman), but a dude wielding all-powerful Infinity Stones is tough to handle — especially when he sets off a Rapture-like event that wipes out many of our heroes.

Looking for more on 'Infinity War'? Listen to The Mothership podcast's spoiler-tastic analysis of the film below.

Kevin Feige, Infinity War producer and Marvel Studios president, promises that certain characters' endings were “necessary” in his expansive ensemble: He acknowledges that these sequences were emotional when he pitched them to the actors in question — years ago, in some cases — and when they were filmed.

“It’s come in waves, the emotions of bringing a lot of these characters’ stories to their conclusion, in all sorts of different ways that word could be defined,” Feige teases. "These characters, in many cases going back decades and decades, would not be around if they never changed or evolved or weren’t updated.”

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Stars from all over the Marvel Universe collided at Monday night's wold premiere of 'Avengers: Infinity War' in Hollywood. Chris Pratt, aka Star-Lord, and Tom Hiddleston (who plays Loki) took a moment to pose with fans at the premiere. Who else was there? Tommaso Boddi, Getty Images for Disney

While fans mourn the loss (at least for now) of some beloved good guys, the three original Avengers are all still alive, kicking and will play integral roles in the as-yet-untitled Avengers 4. But the clock is ticking.

Evans, now starring on Broadway in Lobby Hero, says he’ll be a part of reshoots later this year but, as of right now, that’s it for his take on Cap. Leaving the Marvel movies “is going to be one of the hardest things I’ve done. It’s all those feelings of graduating high school or college or just the passage of time. (Like) when you leave an apartment that you’ve lived in for a long time.”

Evans figures he’ll be “a little bit of a basket case" on the final day of filming. "It’s going to be really, really, really hard to know it’s the last time you’re putting the suit on.”

Hemsworth’s Marvel contract is up as well, and while he’s not ruling out a return appearance in the MCU’s upcoming Phase 4, the Australian actor had “this weird sort of nostalgic sadness coupled with joy” through a lot of the recent Avengers filming. “I know that sounds a little wanky, but I don’t know. Maybe it’s just me getting a little more sentimental as I get older and having kids, but you just realize if you don’t look around and appreciate it, life moves pretty damn quick.”

Infinity War and its 2019 follow-up are “closing the circle, for sure,” Downey says. “Strangely, here’s how twisted I am: I’m learning about real life through these movies. Some things are going to remain heartbreakingly unresolved.”

He’s always surprised to see the twists and turns: “I’m basically at this point just happily running plays and suiting up and trusting the process,” he says. However, “if Iron Man’s gonna hang up his jersey or whatever comes down from on high, I feel like everything is being left in very capable hands.”